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class: center, middle

# Hexagonal Architecture

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# Also known as

* Ports and Adapters
* Clean Architecture
* Onion Architecture

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# Layered architecture problems

* No clear application core
* Business logic leaks to the presentation layer
<br />  
<br />  

.center[![Alt text](layers.png)]

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# Intent

* Application can be driven by users, programs, automated test or batch scripts
* Application can be developed and tested in isolation from its eventual run-time devices and databases

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# Applicability

Use Hexagonal Architecture pattern

* When the application needs to be independent of any frameworks
* When it is important that the application highly maintainable and fully testable

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# Concepts

* Ports are interfaces
* The ports that drive the application are called primary ports
* The ports that are driven by the application are called secondary ports

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# Concepts

* Adapters are interface implementations
* Typically different adapters for testing and production are provided

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# Diagram

.center[![Alt text](ports_and_adapters.png)]

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# Real world examples

* [Apache Isis](https://isis.apache.org/) builds generic UI and REST API directly from the underlying domain objects

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# Tutorials

* Blog http://java-design-patterns.com/blog/build-maintainable-systems-with-hexagonal-architecture/
* Source code http://java-design-patterns.com/patterns/hexagonal/

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